This invention relates to liquid sterilizers and more particularly to water sterilizers employing ultra-violet radiation to kill bacteria.
It is well known to sterilize water by exposing the water to ultra-violet radiation at a wavelength of approximately 2537 Angstroms. In a typical sterilizer, water is exposed to ultra-violet radiation as it is introduced through an inlet into a cylinder housing an ultra-violet tube, the water then flowing through the length of the cylinder where it exits through an outlet. The water is sterilized as it is exposed to the ultra-violet radiation generated by the tube.
It is also known to sterilize water by exposing the water to ozone generated at a wavelength of approximately 1880 Angstroms. The ozone can be generated by means of a tube of similar construction to that of an ultra-violet radiation generator, or by means of an electrical arc generated in the water. The known ozone generator leaves a residue of ozone in the water, which continues to sterilize the water as it passes through the cylinder.
It is also possible to sterilize water utilizing gamma ray radiation. Thus, the principles of this invention apply to all of these known kinds of sterilizers. However, the invention will be specifically described with reference to embodiments employing ultra-violet radiation.
Although sterilization of water by use of ultra-violet radiation has an excellent reputation for killing bacteria, such sterilizers have tended to be expensive, and also require specialized skills for installation and maintenance. However, there is a need for a water sterilizer that a home or cottage owner can afford and can install and maintain without having specialized skills.
One of the problems associated with known sterilizers, which contributes to their complexity, is that they are designed as permanent installations, except for the replacement of worn out or defective bulbs. As a consequence, these sterilizers have complex mounting arrangements for the tube, the end seal connections and the water inlet and outlet. Also, because the known sterilizers were designed as permanent installations, the water supply connections tended to be complex, again requiring specialized skills for installation. Since the tubes are also quite delicate, there is a serious risk of tubes being broken on replacement, if done by anyone other than a trained technician.
An example of a prior art sterilizer of complex design is described in Canadian Pat. No. 610,989, which issued to Corn Products Company on Dec. 20, 1960. This patented sterilizer was clearly designed as a permanent installation except for replacement of the ultra-violet tubes. For example, the inlet and outlet ports are formed of conduits, nipples, adapters, gaskets and screws. The ends of the ultra-violet tubes are connected to electrical sockets that are mounted on connector blocks slidably mounted on connector block plates and locked in place. When a tube is to be replaced, these connectors have to be removed from the connector blockplates. It can be readily appreciated that specialized skills are thus required both for initial installation and maintenance. Resealing of the sterilizer when replacing a lamp also poses a problem.
As is well known, ultra-violet tubes operate more efficiently at higher temperatures. One known type of water sterilizer, therefore, provides a protective quartz sheath surrounding the tube, thereby leaving an air space between the sheath and the tube to provide insulation for the tube from the water flowing around the sheath. However, such sheaths suffer from the disadvantage of having to be cleaned periodically to remove collected dust, which can inhibit the penetration of light from the tube through the sheath to the water, resulting in reduced efficiency and risk of non-sterilization. Thus, the cleaning of the sheaths has to be done by a skilled technician. Special handling is also required, especially because the quartz is susceptible to finger prints, and because the quality of quartz required produces a fragile sheath that can be broken very easily. From the above discussion, it can be appreciated that prior art water sterilizers employing sheaths are expensive and require specialized skills for their installation and maintenance. Canadian Pat. No. 610,989 employs such a quartz sheath, adding to the complexity, fragility and cost of the sterilizer.
Other known prior art sterilizers employ sensing devices to sense the amount of light radiated by the ultra-violet tube, coupled with an electro-magnetic control device to control valves at the water inlet. Thus, if the tube is not emitting sufficient light to sterilize, the valve at the inlet is closed and the unit fails safe. Although serving a useful purpose, such fail safe devices add to the expense of a sterilizer unit. A prior art sterilizer employing such a fail safe device is described in Canadian Pat. No. 674,555, which issued to Allsafe Water Sterilizer Ltd. on Nov. 19, 1963. The Allsafe sterilizer is another example of one employing a protective sheath and designed as a permanent installation except for replacement of lamps, again involving a complex mechanical end cap arrangement requiring specialized skills for maintenance.
Canadian Pat. No. 767,856 granted Sept. 26, 1967 and Canadian Pat. No. 841,135, granted May 5, 1970, and invented by James W. Harrison, are further examples of sterilizers that are designed to fail safe. The sterilizers described in these patents are of the permanent installation type requiring the removal of end caps for replacement of ultra-violed tubes.
I am also aware of the sterilizers disclosed in Canadian Pat. No. 357,083 issued Apr. 7, 1936 to James et al. and No. 739,145 issued July 26, 1966 to Filion.
My application Ser. No. 781,021 referred to above discloses a disposable unit that consists essentially of an elongated tube for generating the sterilizing radiation and a similarly shaped outer jacket opaque to the radiation. The tube extends coaxially along the jacket while forming a flow chamber between them, i.e. between an outer cylindrical surface of the tube and an inner cylindrical surface of the jacket. Water is caused to travel along this flow chamber from an inlet at one end of the jacket to an outlet at the other end. The quartz sheath that had traditionally been located around the tube in the majority of prior art constructions (see for example Canadian Pat. No. 610,989 referred to above) has been omitted from my prior construction, the water coming into direct contact with the tube surface. This omission of the intermediate quartz sheath represented a significant cost saving and was largely responsible for the ability to make the unit a disposable one. By reference to "disposable" it is intended to state that the tube is or can be non-removably mounted in the jacket by means of liquid tight seals at each end, so that when the tube is burnt out the whole unit is discarded.
In the specific form of unit disclosed in my said earlier application (patent), the ends of the tube project beyond the ends of the jacket in which they are mounted. These projecting tube ends providing terminals that serve both for establishing the necessary electrical connections and for mechanically supporting the unit in an outer protective casing.
In using a "disposable" unit, no attempt is made to remove a used tube from its jacket. Once a year or as found necessary, the whole unit is removed from the casing and discarded, and a new unit is fitted. This operation can be carried out by an unskilled person as easily as changing an electric light bulb. Such an operation contrasts with the practice prior to my earlier invention, which involved the services of a skilled technician to remove the old tube from the jacket and replace it with a new one, while handling the quartz sheath very carefully. Even so it was often found impossible to avoid breakage of the quartz sheaths.
My prior development was thus a significant step forward in the art, in that it reduced the cost of each unit (jacket and tube) and simplified the mounting thereof in a casing. This simplification was sufficient to render it economically preferable to treat each unit as a disposable one and thus avoid the need for the services of a skilled technician. As a result, my prior development has already enjoyed significant success in the market place.
However, the direct contact between the water and the tube that resulted from elimination of the quartz sheath has one disadvantage along with its many advantages. Apart from the cost advantage of a disposable unit that has already been discussed, another advantage was elimination of the condensation and dust build up that had previously been experienced in the air space between the tube and the sheath.
The disadvantage, on the other hand, arose from the fact that the direct contact between the often cold incoming water and the tube could sometimes lower the temperature of the tube below its operational optimum, thus reducing the amount of ultra-violet emission. In practice, this problem could lead to the use of a tube larger than that normally required, in order to have sufficient spare capacity to be able to compensate for the lowered efficiency of the tube under adverse temperature conditions.
The present invention is an improvement over my prior development described above, in that it avoids this disadvantage without going back to the problems of the earlier sheath-type of construction. In other words, the present invention retains the essential merits of my prior development, i.e. cheapness and ease of installation and hence disposability, while at the same time recapturing and improving upon an advantage afforded by the sheath type design, namely thermal insulation of the tube from cold incoming water.
This aim has been achieved in the present invention by making the tube a double-walled tube, i.e. a tube having inner and outer cylindrical walls sealed together and spaced apart from each other so as to define a sealed space between them. The outer surface of the outer wall is in contact with the liquid in the flow chamber defined between the tube and the jacket, while the conventional means for generating the radiation is located within the inner wall. As a result, the intermediate space, which may be evacuated, provides thermal insulation between such generating means and any cold liquid in the flow chamber.
For a fuller understanding of the nature and advantages of the invention, reference should be had to the ensuing detailed description taken in conjunction with the accompanying drawings.